For most workers, the tax cut windfall will disappear

Millions of workers have received a small cut of Corporate America's tax cut bonanza. Unfortunately, the windfall for most workers will be fleeting.

53% of the investments in workers announced by Russell 1000 companies have been one-time bonuses, according to an analysis shared exclusively with CNNMoney by the nonprofit group JUST Capital.

In other words, most of the benefit to workers will beshort-lived.

Another 6% of the worker windfall has been in the form of one-time contributions to employee 401(k) plans, JUST Capital found after examining announcements by 93 companies in the Russell 1000. The index is home to 1,000 of the largest US public companies.

Less than one-third of the investment in workers will be permanent. JUST Capital found that 29% of the money is going toward wage hikes, while another 2% is being set aside for ramping up 401(k) programs by raising matching contributions.

"A permanent wage increase sends a stronger signal of investing in your workforce than a one-time bonus," said Martin Whittaker, CEO of JUST Capital, which fights for equal treatment of workers. The nonprofit was founded in 2013 by a group that includes hedge fund billionaire Paul Tudor Jones, Arianna Huffington and Deepak Chopra.

"If you're struggling to make ends meet stacking shelves at Home Depot, would you rather get a one-time bonus or a permanent wage increase?" Whittaker said.

Home Depot(HD) is among dozens of major companies that announced $1,000 tax cut bonuses for workers after the tax cut became law in late December. Bank of America(BAC), Verizon(VZ), Comcast(CCZ) and Pfizer(PFE) did the same.

Other companies, such as Wells Fargo, FedEx(FDX) and JPMorgan Chase(JPM), have opted for a more lasting benefit in the form of higher wages. And some companies including Starbucks(SBUX), Walmart(WMT) and PNC Financial(PNC) handed out one-time bonuses as well as pay raises.

About 10% of the worker investments announced so far aregeneral benefits such as improved vacation policy, health care policies or skills training. For instance, Boeing(BA) announced plans to spend $200 million on retraining and other worker benefits.

Of course, any benefit from employers is on top of personal tax cuts Americans have seen from the tax law.

"Stock buybacks are purely for the shareholder," said Ian Winer, head of equities at Los Angeles-based Wedbush Securities. "It is very difficult to argue buybacks are good for the overall economy or average worker."